1. Field of the Invention
This invention relates to an image forming apparatus or nonimpact printer that applies one or more forms of energy to an ink or dye ribbon or the like to cause the transfer of a selected portion thereof to a substrate to form an image. More precisely, this invention relates to nonimpact printers that accommodate more than one ribbon at once, and especially printers that permit use of one or more energy sources with two or more ribbons, which can be of differing types, including various types of combination ribbons, and to means for switching from one ribbon or energy source to another in the course of a printing task. Also included are printers that accommodate direct energy printing along with processes that employ a transfer medium.
2. Background Information
In thermal transfer printing, an ink-bearing ribbon is pressed against a substrate between the thermal print head and a platen. The substrate can be ordinary or specially coated paper, or also plastic film, acetate and the like. Resistor elements in the print head are selectively subjected to a heating current, thereby causing the transfer of ink from the ribbon to the substrate in a desired pattern. In the analogous electroresistive process, the print head uses needle-like electrodes brought into contact with an electroresistive ink to cause such transfer. In either case, for black printing, a single long black ink ribbon can be used, or a single ribbon might include a multiplicity of black panels, each of the size (e.g., 81/2.times.11 inches, legal size, or A4 etc.) of the substrate onto which the image is to be transferred. For color printing, three separate panels in the colors yellow, magenta, and cyan, typically arranged in repetitive units along the ribbon, are generally used. A full color image is obtained from the three primary colors by printing one color over the other, typically in the order yellow, magenta and cyan.
The three colors can also be superimposed to produce a black image, but such an image is usually not of the same quality as can be formed using a single black ink. To use three color panels to produce a black image is also wasteful of color panels, and increases the time required for the image transfer. To obtain the generally higher quality black image available from a black ribbon requires replacing the three-color ribbon with a black ribbon (and back again to do full color printing, etc.), and to avoid repetitive ribbon changing, ribbons have been developed in the prior art that include black panels in addition to the three color panels.
U.S. Patent Appl. Ser. No. 08/039,871 filed Mar. 30, 1993 entitled COMBINATION INK OR DYE RIBBON AND APPARATUS FOR NONIMPACT PRINTING by the inventor of the present invention describes "combination ribbons" which, in addition to three-color and black panels, also include different types of panels, e.g., thermal transfer, dye diffusion, electroresistive, and other types that are needed for different printing requirements. It thus becomes possible to carry out various kinds of printing using just one ribbon.
One disadvantage of the foregoing procedure, however, is that of needing to traverse through the ribbon in order to arrive at a black ink panel, move back again to do color printing, go back to the black panel or to another panel type, and so on. Such a process is wasteful of time and can be damaging to the ribbon. Moreover, the relative amounts of full color and black or other printing required may not coincide with the relative numbers of different panel colors or types on the ribbon, so that some portions of the ribbon may become wasted.
One solution of the foregoing problem has simply been to employ two printers: one having a three-color ribbon for full color printing, and another with a black ribbon for printing in black. However, that procedure introduces extra expense, and also requires additional desk space. Moreover, for images that require black printing along with full color printing, to obtain the higher quality black image from the black ink printer it becomes necessary to transfer the substrate onto which the image is to be placed from one printer to the other, and it may be difficult or impossible to obtain the same substrate alignment (i.e., image registration) in the one printer as in the other, so that the image transferred in the second printing will actually appear where desired relative to the first image. The alternative procedure of using just one printer but changing ribbons for each kind of printing process, while saving of expense and desk space, introduces even greater operator inconvenience.
Another type of thermal transfer printer has a back roller in lieu of a platen, so that the back roller faces against the thermal head with the ink donor sheet or ribbon and the recording sheet or receiving medium pressed therebetween as usual, but wherein the back roller is driven by a motor so as to advance both the ribbon and receiving medium. U.S. Pat. No. 4,495,507 issued Jan. 22, 1985 to Moriguchi et al. describes such a device that contains two complete "recording stations," i.e, two separately functioning back rollers, roller drive motors, thermal heads and ribbons (on associated supply and takeup rolls) wherein the two ribbons provide twocolor printing onto a receiving medium that is made to pass first through one recording station and then through the other. This "two-station" design also has registration problems, namely, that any difference in diameter between the two back rollers will cause differences in the rate of advance of the receiving medium in the two cases, thereby introducing a color shift in the transferred image. The Moriguchi et al. patent addresses that problem by using different drive motors so that one motor can compensate for such variations in the rate of medium advance, but even so, the use of two recording stations in a back roller device that advances both the ribbon and receiving medium does not resolve the problems discussed above, especially in that the Moriguchi et al. device is fixedly disposed whereby the receiving medium must pass through both stations whether or not such double printing is desired. (In the case that double printing was not desired, presumably the receiving medium and ribbon would be advanced in the second station as before but no signal would be sent to the print head, hence the amount of ribbon so advanced would be wasted.)
In U. S. Pat. No. 4,774,527 issued Sep. 27, 1988 to Hancock et al., a thermal print head is described that incorporates at least two oppositely facing columns of electrodes such that the print head can be removed and replaced in an oppositely facing direction when one column of electrodes has become worn out through use, or the two different columns may also have different sized electrodes for printing at different levels of resolution. The different sets of electrodes are connected to same-sized sets of conductors, and those conductors are alternatively connected to a samesized set of contact pads on a connecting cable, so that which set of electrodes is in use depends upon the orientation in which the print head is mounted in the printer, i.e., as to which set of conductors contacts those contact pads, whereby one or the other set of electrodes will also be brought into contact with the printing ribbon when the print head is mounted. Reversal of orientation of the print head requires removal thereof and reinstallation.
Another disadvantage of the Hancock et al. device is that although only one set of electrodes is being used at a time, the image signal is sent also to a second or more sets of electrodes, thus subjecting the same to thermal cycling from the image signal and causing unnecessary deterioration thereof. It would be preferable to provide a switching system that would connect the image signal only to the electrode set in use, and secondly to provide means for moving that structure into a selected position or orientation that places the desired set of electrodes at the image receiving medium for printing without the need to remove and reinstall the entire electrode structure.
In U.S. Pat. No. 4,626,870 issued Dec. 2, 1986 to Yamamoto et al., another print head is described that has two sets of thermal elements thereon, the two sets being of different resolution in terms of dots per inch. In this case, the print head is formed of two halves bent crosswise to a small (e.g., 3 degrees) dihedral angle at the center thereof, and the two sets of thermal elements are disposed on either side of the central bend line, either immediately adjacent thereto or symmetrically at opposite ends of the print head away from the central bend line. The print head is used so that the two sets of thermal elements are in contact with a thermal transfer ribbon at the same time, and one or the other set, and thus the resolution in which a character is printed, can be selected by appropriate electronic signals. Since the two sets of thermal elements have different lateral positions on the print head, it appears that the positioning of the print head relative to the thermal transfer ribbon, or more exactly in relation to a substrate onto which an image is to be transferred, must also be adjusted in selecting one or the other set of thermal elements.
In the prior art, two print heads and two ribbons have been used for two color printing. For full color printing, three color (y, m, c) ribbons have been used, or four color (y, m, c and black) ribbons for full color and black printing, and each of these procedures has had inherent registration problems. To help avoid those problems, and for the other purposes described herein, what is needed and would be useful is a method, within one printer, of using a y, m, c (and black) ribbon with good registration for full color (and black) printing in a single operation while also, when precise registration is not required, e.g., when inserting a full color image onto a sheet on which a text image will also appear elsewhere, of printing those two images on a single sheet by separate operations.
The foregoing is provided in the present invention, which uses either a single or double energy source (for purposes of different resolutions or printing technologies, etc.), that will also accommodate direct energy printing and/or two or more ribbons as well as a single ribbon; e.g., one for full color printing and one for black printing; one for thermal printing and the other for dye diffusion printing; or one for precoat printing and the other for full color printing over the precoat when printing on rough paper is required; and other examples are given below.. Such a energy source should also be capable of encountering a selected ribbon, as by rotation or a similar simple motion from one to the other under motor control, without need for manual entry to the printer and manipulation of the energy source.
That is, in general the printer is made to accept one or more pairs of ribbons and substrates for which appropriate energy sources are also provided, the operating parameters are set (preferably automatically) for each selected combination, and the particular energy sources, ribbons and substrates are activated as required, so as to provide optimum printing capability for each printing task.